As is generally known, silicone polymers are quite unlike the other organic polymers in having several unique properties. For example, in the case of the silicone rubbers, those can retain their rubber elasticity even at high temperatures over a long period of time, and the rubber elasticity cannot be lost even at a temperature as low as -70.degree. C., with the rubber-like properties changing little with temperature. Further, the silicone rubbers show stable electrical properties over a wide temperature range, and have excellent arc resistance, corona resistance, weatherability, etc. Furthermore, the silicone rubbers undergo no deterioration in rubber-like properties even through long-term outdoor exposure, irradiation with ultraviolet rays, or exposure to an ozonic atmosphere. As described above, the silicone polymers have excellent properties necessary for rubber materials, and due to this fact the polymers have been spread throughout almost all the industrial fields, where the polymers are valued as essential materials.
However, the silicone polymers are inferior in strength to other organic polymers. For example, room temperature-curable silicone rubber compositions which are used as sealants for outer walls of buildings, etc., are not employable as a structural material due to their poor strengths, and their use is limited to sealants. As described above, because of their low strengths, the silicone rubbers have a disadvantage that they cannot be used as a general-purpose resin or an engineering plastic and their use is restricted to special purpose of use only.
Room temperature-curable silicone rubber compositions are also used, due to their in-site forming properties, as formed in-place type gaskets (FIPG) for the sealing around automobile engines. This application is favorable for inventory control and production efficiency and is also advantageous in sealing properties and heat resistance. However, the oil resistance of the gaskets formed from the silicone rubber compositions is insufficient, so that oil leakages occur when newly developed gear oils containing large proportions of additives are used, and this has become a problem.
In attempts to solve those problems of the silicone rubbers, JP-A-59-80463 proposes a method for improving the oil resistance but there is no description therein concerning improvement in the strength, and JP-A-60-219284 proposes methods for improving the oil resistance and also lowering the elasticity modulus but fails to teach a method for obtaining a silicone rubber having a sufficiently high strength. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)